Known in the art is a pneumatic conveying apparatus for unloading cement carriers, comprising a suction line with a vacuum pump connected to a settling chamber and an intaking nozzle, a discharge mechanism, and an electrically driven nozzle-transfer mechanism (cf. "Handling Operations on Transport" by N. Sosunov et al, State Publishing House on Ferrous & Non-Ferrous Metallurgy, Moscow, 1962, pp. 83-84). In the apparatus, the electrically driven nozzle-transfer mechanism constitutes a manually operated electrical hoisting tackle. The uniform material intake, which is a controlling factor in a steady-state operation of the apparatus; cannot be achieved by an operator in charge of the hoisting tackle. A steady contact between the remotely-controlled and visually supervised intaking nozzle and the bulk material is hardly ever attained: now and then the nozzle buries too deep into the material, whereas at times the contact is lost altogether.
This disadvantage has been obviated in a pneumatic conveying apparatus for unloading bulk materials from railway cars (cf. USSR Inventor's Certificate No. 211,385), comprising a suction line formed by a vacuum pump connected to a settling chamber and to an intaking nozzle, a discharge mechanism connected to the settling chamber, and an electrically driven nozzle-transfer mechanism. The nozzle-transfer mechanism is designed as running wheels powered with an electric motor with a power switch. Placed ahead of the intaking nozzle is an electric drive controlling device made in the form of spring-loaded feelers kinematically linked to the power switch of the motor. For the conveyed material to be dilated, a screw conveyer is placed immediately upstream of the intaking nozzle. With the nozzle travelling, the feelers come into contact with the material to shift the feelers, shut down the motor and bring the nozzle to a stand-still in the event, wherein the density of the material is so high that the pressure exerted upon the feelers tends to become larger than the spring force. At the same time the screw conveyer keeps dilating the material until the density thereof is low enough to let the feelers restore their original position, whereupon the motor is started up and the intaking nozzle resumes its travel into the material.
Thus, in the prior art apparatus, a steady contact between the nozzle and the material is attained automatically. The intaking nozzle therewith travels at a constant speed, making occasional stops whenever the material density tends to build up in excess of a desired value.
It will be readily understood by those skilled in the art that ultimate conveying throughout requires some optimum concentration of the conveyed material in the air, depending upon both material characteristics and travelling speed of the intaking nozzle. Since the characteristics of the material, however, vary with the type thereof, transportation and storage conditions, humidity, etc. the optimum concentration of the material in the air can be maintained but by variations in the nozzle travelling speed.
The disadvantage of the prior arrangement consists in a constant travelling speed of the intaking nozzle with no regard to physical properties of the material conveyed, resulting in poor conveying throughput.